Embodiments of the present invention relate generally to blowout preventers, and more particularly, to a method and system to monitor the position of a pipe in a blowout preventer.
Oil and gas field operations typically involve drilling and operating wells to locate and retrieve hydrocarbons. Rigs are positioned at well sites in relatively deep water. Tools, such as drilling tools, tubing and pipes are deployed at these wells to explore submerged reservoirs. It is important to prevent spillage and leakage of fluids from the well into the environment.
While well operators generally do their utmost to prevent spillage or leakage, the penetration of high-pressure reservoirs and formations during drilling can cause a sudden pressure increase (“kick”) in the wellbore itself. A significantly large pressure kick can result in a “blowout” of drill pipe, casing, drilling mud, and hydrocarbons from the wellbore, which can result in failure of the well.
Blowout preventers (“BOPs”) are commonly used in the drilling and completion of oil and gas wells to protect drilling and operational personnel, as well as the well site and its equipment, from the effects of a blowout. In a general sense, a blowout preventer is a remotely controlled valve or set of valves that can close off the wellbore in the event of an unanticipated increase in well pressure. Modern blowout preventers typically include several valves arranged in a “stack” surrounding the drill string. The valves within a given stack typically differ from one another in their manner of operation, and in their pressure rating, thus providing varying degrees of well control. Many BOPs include a valve of a “blind shear ram” type, which can serve to sever and crimp the drill pipe, serving as the ultimate emergency protection against a blowout if the other valves in the stack cannot control the well pressure.
In modern deep-drilling wells, particularly in offshore production, the control systems involved with conventional blowout preventers have become quite complex. As known in the art, the individual rams in blowout preventers can be controlled both hydraulically and also electrically. In addition, some modern blowout preventers can be actuated by remote operated vehicles (ROVs), should the internal electrical and hydraulic control systems become inoperable. Typically, some level of redundancy for the control systems in modern blowout preventers is provided.
During a blowout, when the valves of the BOP are activated, the shear rams are expected to sever the drill pipe to prevent the blowout from affecting drilling equipment upstream. The shear rams are placed such that the drill pipe is severed from more than one side when the valves of the BOP are actuated. Although BOPs are an effective method for preventing blowouts, the rams can sometimes fail to sever the drill pipe for several reasons including lateral movement of the pipe inside the BOP, and presence of a pipe-joint in the proximity of shear rams.
Given the importance of BOPs in present-day drilling operations, especially in deep offshore environments, it is important for the well operator to have confidence that a deployed BOP is functional and operable. Further, it is also desirable for the well operator to know the position of the pipe with respect to the BOP. In addition, the operator would also find it useful to determine the nature of movement of the pipe in the BOP.
As a result, the well operator will regularly functionally test the BOP, such tests including periodic functional tests of each valve to detect the presence of tool-joints in the BOP, periodic pressure tests of each valve to ensure that the valves seal at specified pressures, periodic actuation of valves by an ROV, and the like. Such tests may also be required by regulatory agencies. Of course, such periodic tests consume personnel and equipment resources, and can require shutdown of the drilling operation.
In addition to these periodic tests, the functionality and health of modern BOPs can be monitored during drilling, based on sensing signals produced by sensing systems placed in the BOP, and indirectly from downhole pressure measurements and the like. However, in conventional blowout preventer control systems, these various inputs and measurements generate a large amount of data over time. Given the large amount of data, the harsh downhole environment in which the blowout preventer is deployed, and the overwhelming cost in resources and downtime required to perform maintenance and replacement of blowout preventer components, off-site expert personnel such as subsea engineers are assigned the responsibility of determining BOP functional status. This analysis is generally time-consuming and often involves the subjective judgment of the analyst. Drilling personnel at the well site often are not able to readily determine the operational status or “health” of blowout preventers, much less do it in a timely and comprehensible manner.
In addition, sensing systems are sensitive to the presence of foreign material in the drill pipe and may produce erroneous results that lead to false positives. Examples of foreign material include, but are not limited to, debris caused due drilling and cutting, or water, or gas bubbles, and the like. Further, changes in environmental conditions may also lead to sensor drifts. The sensor drift may cause changes in output of the sensing systems thus causing errors in determination of position of the pipe in the BOP.
Since the corrective actions required to enable efficient operation of the BOP are dependent on determination of the pipe location with respect to the BOP, it is important for the sensing systems to produce accurate results. Hence, there is a need for a method and system that aids in determination of pipe location in a BOP while factoring movement of the pipe as well as the presence of pipe-joints in the BOP.